I agree with the other posters - temperature and humidity have nothing to do with calorie burn. Speed doesn't have a big impact either - it is total distance covered that is the major factor.
In terms of hills, there is roughly an 8:1 ratio in terms of climbing. So 100 vertical feet would represent an additional 800 feet (or 0.15 miles) on the horizontal, in terms of effort. mapmywalk.com has a feature that allows you to track elevation changes.